Miss Floribunda: Leapin’ leafhoppers! Don’t be naive about native plants

Dear Miss Floribunda,

Is it possible for a native plant to get a weird disease like the one you wrote about for roses last month? My coneflowers have developed something that looks a little like the witch’s broom on that photo of a diseased rose I saw last month in your paper (see attached coneflower photo). You wrote that native roses don’t get this disease, so I just assumed that other native plants wouldn’t get it either. What is causing this? What can I do about it?

Cone-fused and Cone-cerned on Kennedy Street

Dear Cone-fused and Cone-cerned,

Cousin Moribunda had no trouble identifying the disease that has attacked your coneflowers: It is called aster yellows. It attacks plants in the Asteraceae family, which includes coneflowers, coreopsis, marigolds, daisies and sunflowers. Aster yellows also attacks carrots, lettuce and celery.

Despite the fact that the symptoms do look similar, the pathogen is not the Rose Rosette Disease virus (Emaravirus rosae) carried by a microscopic eriophyid mite (Phyllocoptes fructiphilus), but Candidatus phytoplasma bacteria transmitted by an insect called a leafhopper (Macrosteles quadrilineatus). Although coneflower rosette mites actually do exist, they cause much less damage to the plant.

Only in early stages could you mistake the two. The less virulent mite does not stunt the growth of the plant, and removing affected flowers is enough to control the disease. In contrast, aster yellows is so devastating that your only recourse is to uproot and dispose of your plants.

You might want to take a look around your yard to hunt for and weed out the common host plants for this insect. These include wild carrot, aka Queen Anne’s lace; wild asters; wild chicory; broadleaf plantain; dandelion; and several thistles.

Despite the beauty of Queen Anne’s lace and the blue flowers of wild chicory, as well as the fact that all these plants are loved by beneficial insects, this invasion means that we must pull them all up, bag them, and throw them out. Again, please don’t leave your coneflowers in the ground, hoping for recovery. Should your coneflower survive, it would become a host plant for next year’s leafhoppers and help spread the disease.

Please don’t resort to insecticides, as you don’t want to kill potential predators of leafhoppers. These predators include many spiders, lacewings, ladybugs, assassin bugs, minute pirate bugs and parasitic wasps. Even neem oil is problematic: If you apply it to plant leaves and stems, you should avoid spraying the oil on the actual flowers, because visiting bees and butterflies will ingest it along with the nectar and pollen.

It is indeed disheartening that popular native plants can be susceptible to this disease. I wonder if you made the mistake of fertilizing them. The possibility of disease in native plants is heightened by fertilization, and most native plants — including coneflowers — don’t need fertilizer anyway.

You might consider planting petunias with your coneflowers, as Moribunda claims they repel leafhoppers. Although nasturtiums are recommended as a trap plant for leafhoppers, she thinks it foolish to grow anything else that might attract these pests to your garden.

It occurs to me that because our large nation comprises areas with radically different growing conditions, it is not entirely reasonable to assume that a plant native to the Great Plains — such as the coneflower — would necessarily be well suited to Hyattsville. Prairie plants like a hot, dry, windy environment.

Even without a leafhopper invasion, our muggy microclimate encourages mildew and other fungal diseases in prairie favorites.

I asked Wendy Wildflower what she grows successfully in her pollinator garden. She told me it is now lush with the tall summer-blooming phlox (Phlox paniculata) native to our East Coast , bee balm (Monarda), wild Carolina petunia (Ruellia caroliniensis), nodding onion (Allium cernuum), obedient plant (Physostegia virginiana), mountain mint (Pycnanthemum) and a number of native grasses she terms “gorgeous.” These are all native to our region.

Please check the Hyattsville Horticultural Society website (hyattsvillehorticulture.org) to find out when the next meeting will take place. All plant lovers are welcome.